Published May 13, 2026 06:00AM
You sign up for a half or full-distance Ironman, put in the training, and are ready for the challenge. Then race day arrives, and somewhere on the run around miles 8-9 or miles 18-20, depending on the distance, it all falls apart.
Long-course triathlons are rarely won on fitness alone. Often, races are lost in the final miles, when athletes run out of steam, get sidelined by gut issues, or seize up with cramps. The easy explanation is poor run fitness. The real answer is usually everything that occurred before the run ever started.
Just because it fell apart on the run doesn’t mean the run is to blame. Every seemingly small, insignificant decision made in the days before the race, every choice on the bike, what you ate, what you skipped, how much you gulped down at the wrong time, adds up.
The hard part is that these errors are subtle, and it’s not always easy to pinpoint what set the ending in motion. These errors don’t wave a red flag or announce themselves. But by the time you notice them, they’re there to stay.
Let’s dig into the nutrition errors that turn a promising performance into a survival shuffle and strategies you can use instead to finish strong.
Fueling errors during the race
Let’s be honest, fueling for a 5- to 17-hour triathlon is complicated. If your race has ever unraveled because of a nutrition mishap, you’re in good company.
Countless factors can derail even the best laid plans, so let’s start with one of the biggest: how you fuel on the bike.
If you remember one thing, let it be this: The run is not fueled on the run; the run is fueled by the bike. What you eat and drink on the bike has the single greatest impact on your run and, ultimately, your race.
Training and fitness matter, but your bike nutrition strategy is what determines whether you finish strong or just finish.
The most common fueling mistakes are starting the race under-fueled and over- or under-fueling on the bike. Grabbing a handful of gels or waiting 30-60 minutes to eat creates an energy deficit that won’t hit you right away, but it will, down the road, on the run.
Over-fueling carries its own risks. Consuming more carbs than your gut is trained for can trigger a cascade of problems. Highly concentrated sports drinks or pushing 120+ grams of carbs per hour without adequate fluids or proper gut training, slow gastric emptying, reduce fluid absorption, and accelerate dehydration. The result: gastrointestinal (GI) distress, or gut shutdown, including nausea, cramps, and bloating.
Your stomach becomes progressively less tolerant as the race goes on. Hoping to catch up on the run? Good luck. Heat, gut fatigue, dehydration, and elevated sympathetic drive all conspire to slow gastric emptying, making it nearly impossible to absorb fuel at the same rate as on the bike.
By the second half of the run, most athletes can tolerate only about half the carb volume they could in the first hour of the bike.
Hydration errors during the race
Carbs in the right amount and at the right time matter, but let dehydration creep in, and everything falls apart.
The balance of fluids and sodium determines whether your carbs even get absorbed. Common hydration errors include drinking to thirst rather than to sweat rate and overhydrating with plain water.
The consequences are brutal: impaired carb delivery to muscles, elevated core temperature and heart rate, and GI distress. Worse, you can’t bounce back from dehydration mid-race.
Without the appropriate balance of sodium and carbs, water alone is an ineffective hydrator and, in excess, can lead to hyponatremia, a dangerous and potentially life-threatening drop in blood sodium.
The fix: Race-ready fueling and hydration
Nutrition planning to avoid late-race blowups starts long before race day. (Photo: Challenge Family)
The longer the race, the more critical your fueling, hydration, and sodium intake become. Water rehydrates, sodium retains, and carbs fuel the body. Together, they target every major limiting factor in endurance performance.
Start fueling within 10-15 minutes of the bike leg. Don’t wait until you feel hungry or “settled” from the swim; by then, you’re already behind. Fuel in smaller, frequent intervals about every 8-15 minutes.
Bike targets:
Carbs: 60–90g/hour, up to 120g/hour with practice and intensity. Aim for the higher end early, when your gut is sharpest.
Fluids: 20-32+ounces, adjust to your sweat rate and conditions. Goal: replace ~85-100% of fluid loss.
Sodium: ~500–1000+ mg/1L water, tailored to individual sweat loss.
Run targets: Plan for a lower-carb intake due to a jostling gut, rising heart rate, and increasing dehydration as the race progresses.
Carbs: 50-70g/hour
Fluids: 20-32+ounces/hour, adjusted to sweat rate. Goal: replace 70-75% of fluid loss.
Sodium: ~500-1000+mg/1L water, tailored to individual sweat loss.
Sweat rate and sodium strategy: Everyone loses fluids and sodium differently. To estimate your sweat rate, compare your pre- and post-session body weight in race-like conditions and intensity.
Unlike carbs and fluids, which you consume at a relatively fixed hourly rate, sodium intake should scale to your fluid consumption. Sodium loss varies widely, but a solid starting point is 500-1000mg per 32oz (roughly 15-30mg sodium per ounce).
Bike hydration checkpoints:
Optimal peeing frequency: Roughly every 2.5 hours indicates good hydration.
Overhydration warning: Frequent peeing or low sodium intake relative to fluid intake.
Underhydration alert: Riding 3+ hours without the urge to pee.
Fuel choice error: Your fuel wasn’t sport-approved
Not all calories are equal. During moderate to high-intensity endurance efforts, fast-digesting carbs are your muscles’ and brain’s preferred fuel source.
If your fuel contains fat, protein, or fiber, or relies on a single carb source, you’re not getting the quick, sustained energy your body needs at race pace. Common offenders include snacks with nut butter, trail mix, and many sports or protein bars.
The fix: The right products
Use properly formulated endurance products that contain multiple transportable carbohydrate sources, specifically glucose and fructose.
The ideal ratio is 2:1 or 1:0.8 glucose-to-fructose, which maximizes absorption at carb intakes over 60g per hour and keeps energy delivery steady. Most modern endurance products are formulated with both, but don’t assume; always check the label for maltodextrin (a glucose source) and fructose to confirm.
Race-day fueling error: Untested in training
You can’t neglect fueling in training and expect to tolerate 120g/hour on race day. The gut adapts like your FTP, gradually with repeated exposure. Testing fuels only a few times or trying a mix of gels, chews, and sports drinks for the first time during the race introduces something new to an already stressed system. It’s a dangerous gamble, with consequences ranging from GI distress and cramping to DNFs.
The fix: Gut training
Start training your gut at least 10 weeks in advance. Begin with shorter workouts, then progressively build to sessions that mirror race-day conditions, duration, intensity, and climate. Start with an hourly carb and fluid intake you can tolerate, and increase by 10-15g every 1-2 weeks, as tolerated.
Gut training tips
Practice at least once per week, and on every long ride and run, including short brick runs. Use the exact gels, sports drinks, chews, or bars you plan to use on race day.
In the heat, lower carb target by 10-20g per hour until fully acclimated, then resume your gut training progression.
Race-day logistics
Consider your bike’s bottle and fuel storage capacity, how you plan to carry or access nutrition during the race, and aid station locations and offerings. If it hasn’t worked in training, it won’t work on race day. That said, always have a backup plan in case of a dropped bottle, missed aid station, or unexpected temperature swings.
Race-day pacing error: Going out too hard
The quickest way to sabotage your race is to ignore your pacing strategy. Starting too fast, even when you feel great, prematurely drains glycogen, accelerates early fatigue, and leaves you struggling to meet energy demands. The result is a painful implosion that was entirely avoidable. Avoid the trap of letting race-day adrenaline dictate your early pace.
The fix: Race-simulated training
In long endurance races, discipline beats ego every time. If you haven’t successfully executed an aggressive start in race-simulated sessions, don’t try it on race day. Start conservative, use perceived exertion as your guide, and trust your training over your emotions. If you feel good later in the race, that’s your cue to build gradually.
Triathlon coach Julie Dunkle recently covered this topic in depth to provide an overview of how to avoid the biggest pacing mistakes in long-course triathlon.
Race week fueling error: Under-fueling
During race week, a reduced training load (taper) is not a green light to slash calories. Top performers maintain a carb-rich diet during training and race week to speed recovery, replenish glycogen, sustain training quality, and preserve gut tolerance.
Cutting carbs or overall energy intake prevents optimal glycogen repletion, leaving you under-fueled and behind before you even start.
The fix: Carb loading
Carb loading is one of the most proven performance strategies, and it’s about more than just a pasta dinner the night before. The goal is to eliminate race-week nutrition landmines, maximize glycogen storage, optimize hydration, and arrive at the start line with a digestive system ready to perform.
Practical race week carb-loading guide:
Increase carb intake to approximately 6-10g carb/kg body weight 48 hours out.
Choose low-fat, low-fiber, easy-to-digest, familiar foods.
Maintain protein intake at 1.6-1.8g/kg body weight.
Hydrate between meals with water mixed with electrolytes.
Test your pre-race breakfast and meals before long training sessions. Adjust until you know exactly what works for your body.
Pre-race breakfast: 2–4 g carbs/kg body weight, 2.5-4 hours before start. Sip fluids with sodium leading up to the race, and bring 20-25g of carbs (gel, chews) to consume 15 minutes before the start.
Bottom line: Use the taper to rest and recover, not cut calories. In the final two days, increase carbs, lower fat and fiber, and stay on top of hydration.
The good news is that every nutritional error covered here is preventable. The athletes who race well aren’t just fitter; they’re better prepared. Fueling and hydration don’t become race-day strengths by accident. Build your strategy in training, test it repeatedly, and arrive on race day with a plan you’ve proven works.